1. Technical Field
The present invention relates to a method of nickel-gold plating and a printed circuit board.
2. Description of the Related Art
In a typical printed circuit board, a copper (Cu) circuit is formed on a copper clad laminate (CCL) and then a nickel layer and a gold plated layer are formed on the copper circuit before a final surface treatment. A nickel plated layer is used as a plating underlayer of the gold plated layer and performs a function of preventing interdiffusion between the copper and the gold plated layer. The gold plated layer intends to reduce an electrical resistance in the part of a substrate coming in contact with an electronic component and to improve bondability between the substrate and the electronic component. The gold plating process is performed in order of oil-removal, soft etching, catalyst, electroless nickel plating and an gold plating.
With regard to the electroless plating, which is one of the methods of treating the surface of the printed circuit board, the nickel plated layer is plated by the electroless method using a reducing agent on a copper plated layer having circuits formed thereon. Then, the gold plated layer is formed on the nickel plated layer by a method of substituting nickel with gold. Local corrosion occurs in a part of the plating underlayer due to a local cell effect generated during the process of the electroless plating. In case the local substitution is excessive in the plating underlayer, a pinhole or discoloration of a plated surface can be observed after forming the electroless plating. Since such an excessive corrosion of the plating underlayer causes the plating underlayer to be diffused into the electroless plated surface, a wire-bonding and a soldering effect, etc., are hereby deteriorated and the reliability of the printed circuit board is reduced.